The flu blanketed the U.S. again last week for the third straight week. Only Hawaii has been spared.

Last week, 1 in 15 doctor visits were for symptoms of the flu. That’s the highest level since the swine flu pandemic in 2009. The government doesn’t track every flu case but comes up with estimates; one measure is how many people seek medical care for fever, cough, aches and other flu symptoms.

Flu is widespread in every state except Hawaii, and 39 states reported high flu traffic for doctors last week, up from 32.

At this rate, by the end of the season somewhere around 34 million Americans will have gotten sick from the flu, the Centers for Disease Control and Prevention said Friday.

(credit: Chris Hondros/Getty Images)

Some good news: Hospital stays and deaths from the flu among the elderly so far haven’t been as high as in some other recent flu seasons. However, hospitalization rates for people 50 to 64 — baby boomers, mostly — has been unusually high, CDC officials said in the report, which covers the week ending Jan. 20.

This year’s flu shot targets the strains that are making Americans sick, mostly the H3N2 flu virus. But exactly how well it is working won’t be known until next month. It’s the same main bug from last winter, when the flu season wasn’t so bad. It’s not clear why this season — with the same bug — is worse, some experts said.

“That’s the kicker. This virus really doesn’t look that different from what we saw last year,” said Richard Webby, a flu researcher at St. Jude Children’s Research Hospital in Memphis.

It may be that many of the people getting sick this year managed to avoid infection last year. Or there may be some change in the virus that hasn’t been detected yet, said the CDC’s Dr. Dan Jernigan, in a call with reporters Friday.

Based on patterns from past seasons, it’s likely the flu season will start to wane soon, experts say. There are some places, like California, where the season already seems to be easing, CDC officials said.

“If I was a betting man, I’d put money on it going down,” Webby said. “But I’ve lost money on bets before.”

The season usually peaks in February, but this season started early and took off in December.

Flu is a contagious respiratory illness. It can cause a miserable but relatively mild illness in many people, but more a more severe illness in others. Young children and the elderly are at greatest risk from flu and its complications. In a bad season, there as many as 56,000 deaths connected to the flu.

In the U.S., annual flu shots are recommended for everyone age 6 months or older. Last seasons, about 47 percent of Americans got vaccinated, according to CDC figures.